Editing Hydrogeology of Burundi

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|Variable Productivity (generally Low to Moderate but sometimes High)

|Variable Productivity (generally Low to Moderate but sometimes High)

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||The productivity of the basement aquifer depends on the localised nature and extent of fracturing and weathering - how thick is the weathered zone and how developed are water-bearing fractures? A thick weathered zone - in some parts of granite and schist basement, such as at Kirundo, this can be up to 100 m (Gutierrez and Barrat 2016) - can provide significant groundwater storage potential. Where tectonic activity has caused increased rock fracturing , such as in fault zones, local basement aquifer productivity can be moderate or high. Fracturing may also, however, act to compartmentalise an aquifer and reduce groundwater flow, which can affect the long-term sustainable yield of a borehole - for example, as suggested in Gitega in central Burundi (Pfunt et al. 2016).

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||The productivity of the basement aquifer depends on the localised nature and extent of fracturing and weathering - how thick is the weathered zone and how developed are water-bearing fractures? A thick weathered zone - in some parts of granite and schist basement rocks this can be up to 100 m - can provide significant groundwater storage potential. Where tectonic activity has caused increased rock fracturing , such as in fault zones, local basement aquifer productivity can be moderate or high. Fracturing may also, however, act to compartmentalise an aquifer and reduce groundwater flow, which can affect the long-term sustainable yield of a borehole - for example, as suggested in Gitega in central Burundi (Pfunt et al. 2016).

BGR have carried out [https://www.geozentrum-hannover.de/EN/Themen/Wasser/Projekte/laufend/TZ/Burundi/burundi_fb_en.html?nn=1546392 hydrogeological studies] of the basement aquifer at sites at Gitega (the second largest city in Burundi), Kirundo and Rumonge.

BGR have carried out [https://www.geozentrum-hannover.de/EN/Themen/Wasser/Projekte/laufend/TZ/Burundi/burundi_fb_en.html?nn=1546392 hydrogeological studies] of the basement aquifer at sites at Gitega (the second largest city in Burundi), Kirundo and Rumonge.

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Data from the Nyanzare wellfield at Gitega where boreholes abstract from fractured zones in the fractured schist and amphibolitic basement indicate that appropriately sited boreholes in the basement aquifer have typical transmissivity values of between 20 and 500 m<sup>2</sup>/day, possibly up to 700 m<sup>2</sup>/day (Tiberghien et al. 2014, Pfunt et al. 2016). Borehole yields of up to 60 m<sup>3</sup>/hour are reported (Gutierrez and Barrat 2016), but compartmentalisation of the aquifer by fracturing suggests that these abstraction rates are not likely to be sustainable (Pfunt et al. 2016). [https://www.geozentrum-hannover.de/EN/Themen/Wasser/Projekte/laufend/TZ/Burundi/burundi_fb_en.html?nn=1546392 BGR] quote transmissivity values of around 35 m<sup>2</sup>/day, and borehole yields of up to 20 m<sup>3</sup>/hour, from the weathered zone of granites at Kirundo. However, more typical borehole yields across most of the basement aquifer are likely to be lower: from around <0.5 to 5 m m<sup>3</sup>/hour (Gutierrez and Barrat 2016).

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Data from the Nyanzare wellfield at Gitega where boreholes abstract from fractured zones in the fractured schist and amphibolitic basement indicate that appropriately sited boreholes in the basement aquifer have typical transmissivity values of between 20 and 500 m<sup>2</sup>/day, possibly up to 700 m<sup>2</sup>/day (Tiberghien et al. 2014, Pfunt et al. 2016). Yields of up to 20 m<sup>3</sup>/hour are reported (Pfunt et al. 2016), but compartmentalisation of the aquifer by fracturing suggests that these abstraction rates are not likely to be sustainable. [https://www.geozentrum-hannover.de/EN/Themen/Wasser/Projekte/laufend/TZ/Burundi/burundi_fb_en.html?nn=1546392 BGR] quote transmissivity values of around 35 m<sup>2</sup>/day, and borehole yields of up to 20 m<sup>3</sup>/hour, from the weathered zone of granites at Kirundo. However, more typical borehole yields across most of the basement aquifer are likely to be lower: from around <0.5 to 5 m m<sup>3</sup>/hour (Gutierrez and Barrat 2016).

Groundwater levels (water table) in the basement aquifer at Gitega are around 15 m below ground level in the base of the valley (Pfunt et al. 2016); they may be deeper at higher elevations.

Groundwater levels (water table) in the basement aquifer at Gitega are around 15 m below ground level in the base of the valley (Pfunt et al. 2016); they may be deeper at higher elevations.

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